Certain polyamines, or compounds containing polyamine substructures, mediate reversal of poly(A) induced inhibition of RNase activity. Effective compounds contain three amino groups, at least two of which are charged and are separated from the others by no less than three carbon atoms. Spermidine and 9-aminoacridines, which contain substituted propyl- or butyl-amino moieties at the 9-amino position and which bear two positive charges per molecule, are efficacious at low concentrations (5 Mu M). A decrease in effectiveness is associated with the removal of one aromatic ring from the 9-aminoacridines. However, the resulting 4-aminoquinolines, unlike the acridines, do not inhibit enzyme activity when present in concentrations above 30 Mu M. Relocating the diamino side chain from the 4- to the 8-position of the quinoline nucleus causes a decrease in charge density to +1, with the result that such compounds are ineffective. The identity of the most effective polyamines depends on the RNase studied. The combination of variable 3'-terminal poly(A) segment length and polyamine identity and concentration constitutes a system by which RNase activities and, therefore, substrate-degradation rates, may be easily varied.